Plant invasive species cause serious impacts for biodiversity and agriculture. The present study aims to develop biological control solutions to limit the impacts of invasive plants in Australia : Sonchus oleraceus and Allium triquetrum. First, surveys will be carried out in Southern Europe to characterize the communities of phytophagous agents present on these plants. This descriptive phase will allow consideration of hypotheses on the interactions in nature between those plants and their potential natural enemies. Second, the work will consist of the characterisation of the food webs, using innovative molecular approaches (e.g. NGS) and a community approach to study the interactions of these natural enemies and their impact on their host plants. Finally, experiments (under controlled conditions) will be carried out to test the hypotheses posed from the second step, to determine the interactions (positive, negative or neutral) between several natural enemies depending on their specific features and host plant characteristics.